Lexion, a bold Greek startup in the heart of Athens, is quietly reshaping the future of space propulsion. While much of the world looks to Silicon Valley or established spaceports for innovation, Lexion is developing radical new technologies that challenge the status quo. At the centre of its mission is APEX — a hybrid propulsion engine designed to overcome the longstanding divide between jet and rocket systems. If successful, it could unlock the era of fully reusable spaceplanes that take off like aircraft and reach orbit without complex staging or heavy fuel loads.

We sat down with Ioannis Alexopoulos, co-founder and CEO of Lexion, to discuss the company’s vision, the inspiration behind their clean-sheet approach to engineering, and what it means to build next-generation aerospace technology far from the traditional powerhouses of the industry. From collaborating with the European Space Agency to dreaming up a new kind of launch infrastructure, Lexion’s journey offers a glimpse into what the future of spaceflight might look like—and why that future might just take off from Greek soil.

What is Lexion, and what is its main vision in the field of space technology?

Lexion is a mechanical and aerospace engineering R&D company based in Greece, dedicated to developing radically novel technologies. Our innovation process begins with a clean-sheet methodology: we approach design from first principles, leveraging fundamental physics and core engineering logic so that we are not constrained by existing technologies. We then integrate multidisciplinary fields such as unsteady fluid dynamics, combustion engineering, and robotics—using a combination of analysis, simulation, and physical testing—to advance concepts from theory to functional prototypes.

While Lexion engages in a broad spectrum of cutting-edge technologies, our primary focus is on developing next-generation hypersonic propulsion systems for aerospace applications. We target the critical gap between high-power, low-efficiency rocket propulsion and highly efficient but relatively low-powered jet propulsion—a longstanding obstacle that has prevented several major breakthroughs, including the realisation of a true Single Stage to Orbit (SSTO) vehicle.

Our long-term vision is a fully reusable spaceplane capable of reaching hypersonic speeds in airbreathing mode before seamlessly transitioning to rocket mode to exit the atmosphere. This approach not only has the potential to drastically reduce the cost per kilogram to orbit but also to enable a new kind of launch infrastructure—more akin to an airport than a launchpad—facilitating frequent, flexible, and low-complexity space operations.

What is the company’s mission, and how does it differentiate itself from others in the aerospace sector?

History has shown time and again that even the most established technologies eventually reach their limits. As new challenges emerge and new capabilities become available, progress demands that old systems step aside to make room for disruptive innovation. Lexion’s mission is not to make incremental improvements to legacy space launch systems but to replace them with fundamentally superior alternatives.

Rockets must carry both fuel and oxidiser onboard due to their inability to utilise atmospheric air, resulting in extremely high initial mass relative to their payload. This makes early-stage acceleration difficult and energetically expensive. To address this, the industry has long relied on multi-stage configurations, where spent stages are jettisoned during ascent. More recently, concepts like ground-based centrifugal launchers have been proposed to bypass part of the initial propulsion burden. However, all of these approaches introduce significant complexity, logistical challenges, and cost—even when partial reusability is achieved.

At Lexion, we pursue a fundamentally different path. We are developing the APEX (Airbreathing Pulsed EXplosions) engine—a hybrid propulsion system that begins as an airbreathing engine, using atmospheric oxygen to drastically reduce launch mass, and then seamlessly transitions to rocket mode to exit the atmosphere. This dual-mode capability eliminates the need for complex staging and enables a new paradigm of reusable, aircraft-like space operations that are more efficient, flexible, and cost-effective.

What is the significance of collaborating with the European Space Agency (ESA) through the ESA BIC Greece program for the development of APEX?

The greatest benefit of joining the ESA BIC program has been the validation of our technology and the recognition of its disruptive potential. Especially in the early stages of such an ambitious project, having our logo displayed alongside that of one of the world’s leading aerospace institutions carries enormous weight—it sends a strong message of credibility.

Beyond the symbolic value, ESA BIC gives us access to an invaluable network that includes technical expertise, testing infrastructure, and a broader European ecosystem aligned with our mission to push the boundaries of space capability through innovation.

It’s also worth noting that the program includes a €50,000 equity-free grant. While this amount represents a tiny portion of our total budget, it reinforces the trust placed in our vision and provides meaningful support as we build the foundations of APEX.

What does it mean for you to develop this kind of technology in Greece, and how could it impact the local space tech ecosystem?

Developing frontier aerospace technology in Greece carries both symbolic and strategic importance for us. Symbolically, it demonstrates that high-impact innovation can emerge from anywhere—even outside the traditional power centres of aerospace. Strategically, we see Greece as a country with growing momentum in the development of its domestic tech startup ecosystem.

Until recently, this ecosystem was largely dominated by business-oriented ventures, with few proprietary deep-tech companies at its core. Funding options were mostly limited to venture capital firms, which tended to avoid high-risk, high-reward projects at the earliest stages. However, this is beginning to change. A new wave of deep-tech startups is now emerging (primarily in biomedical sectors), while private investors are becoming more open to supporting breakthrough technologies. At the same time, the Greek state is actively promoting technological excellence through initiatives such as the creation of the Hellenic Center for Defence Innovation (HCDI).

This shift reflects a broader transformation in Europe’s approach to innovation—gradually embracing more liberal methods and recognising the strategic importance of developing its own cutting-edge technologies rather than relying solely on allies. Europe still has a long way to go, but in our view, the most important step is already underway: acknowledging the problem and committing to bold change, even when catalysed by difficult geopolitical realities like the war in Ukraine.

In Greece, we are also fortunate to collaborate with key partners such as the National Technical University of Athens (NTUA), which not only provides the scientific infrastructure to support highly demanding engineering work but also connects us to an international network of collaborators.

Finally, Greece’s strategic relationships with major aerospace powers such as France and the United States, combined with our direct engagement with the European Space Agency, position us well to collaborate with international partners whenever it aligns with our goals.

We also hope that our efforts will encourage other organisations to engage in deep-tech ventures targeting aerospace applications, and that we will actively contribute to the creation of domestic infrastructure for the development of high-speed propulsion technologies.

How do you see Greece’s position in the global space technology landscape, and what role does Lexion play in it?

Greece’s domestic space ecosystem is in a phase of gradual development. In recent years, we’ve seen the emergence of a more structured national strategy, including the launch of programs like the Greek microsatellite initiative. Most current activity focuses on satellite data processing, downstream services, and the development of space-grade electronics. However, Greece remains largely absent from truly game-changing domains—such as hypersonics and next-generation propulsion—which continue to be pursued by only a handful of entities worldwide.

That said, the global space landscape is evolving rapidly. With the advent of enabling technologies such as 3D printing and artificial intelligence, the barriers to entry for advanced aerospace R&D have been significantly lowered. Today, even smaller companies in countries like Greece can begin experimenting with frontier technologies without the colossal capital requirements of the past.

For a newly founded company like Lexion to gain a foothold in such a competitive industry, proprietary innovation is essential—but it is not enough. Turning breakthrough ideas into real-world systems requires three additional pillars: significant funding, a favourable regulatory and policy environment, and deep technical expertise.

On the first two fronts, both Greece and the broader European ecosystem are moving in the right direction—investing in R&D, updating institutional frameworks, and laying the groundwork for long-term innovation. While the gap with the United States remains considerable, we are cautiously optimistic about the direction of change.

The third element—technical know-how—presents a greater challenge. Greece currently lacks a domestic talent pool with direct experience in hypersonic propulsion and related technologies. For this reason, we actively seek support from ESA-affiliated partners and aim to tap into the global academic network of Greek diaspora engineers and scientists. Our goal is to build a team of experts—either in-house or through strategic collaborations—capable of bringing APEX to life and anchoring high-speed propulsion research within Greece. In fact, within the next month, we will be announcing an open senior engineering position as the next step in expanding our core technical team.

What is the APEX engine, and what makes it innovative compared to traditional propulsion systems?

There are three major categories of propulsion systems used for atmospheric and spaceflight, each with its own advantages and limitations.

First, we have turbojet and turbofan engines—the kind used in most aircraft. These systems offer a good balance of thrust-to-weight ratio and efficiency, but they are limited in speed, typically operating below Mach 2–3 due to thermal, aerodynamic, and mechanical constraints.

The next category includes ramjet and scramjet engines. These are designed for much higher speeds and use the vehicle’s own velocity to compress incoming air, eliminating the need for rotating compressor blades. This makes them mechanically simpler, but they can only generate thrust once the vehicle is already moving at speeds above Mach 3. As a result, they cannot operate from a standstill and require a separate engine to bring the vehicle up to speed—making the overall propulsion system more complex.

The third category consists of rocket engines. Rockets can operate from zero velocity all the way to orbital speeds and beyond. Unlike airbreathing engines, they don’t depend on atmospheric oxygen, which makes them ideal for spaceflight. However, they come with major challenges: extremely high pressures and temperatures, high fuel consumption, and the need to carry both fuel and oxidiser from launch—leading to massive initial vehicle mass and lower efficiency.

The APEX engine is designed to bridge this gap. It is a hybrid propulsion system capable of operating efficiently across a wide range of flight regimes, from takeoff through hypersonic speeds and into space. Thanks to its novel pulsed-combustion architecture, APEX functions in three distinct phases:

During takeoff, it operates like a turbofan, using atmospheric air to generate thrust from a standstill.

As the vehicle surpasses Mach 2, the air inlet geometry shifts, and the engine transitions into ramjet mode, using forward velocity to compress incoming air.

At high altitudes and speeds beyond Mach 5, APEX enters rocket mode, using an onboard oxidiser to continue propulsion outside the atmosphere.

This integrated, mode-shifting approach improves propulsion efficiency compared to conventional rocket-only systems and significantly reduces mission complexity by eliminating the need for multiple propulsion stages or external boosters.

What are the next steps for Lexion, and what are your long-term ambitions in space technology?

We have already built a functional model of the APEX engine as a proof of concept. At this stage, we are conducting a full parametric optimisation of all the engine’s subsystems, with the goal of constructing a refined new prototype within the next two years.

A major challenge lies in the fact that APEX operates using a fundamentally novel combustion process. As a result, existing empirical data—which is critical for CFD simulations—cannot always be applied reliably. This requires us to develop new computational models and custom experimental setups in order to generate fresh datasets that accurately reflect the engine’s physical behaviour.

Once this optimised prototype is completed and tested in a certified laboratory, we plan to proceed with the development of a full-scale engine. In parallel, we are also exploring licensing opportunities for the technology in non-aerospace sectors. Given the engine’s unique thermodynamic cycle, we are investigating its application in maritime propulsion, hydrogen-based power co-generation systems, and jet-powered VTOL vehicles.

For example, as environmental regulations tighten in port areas, vessels increasingly rely on a secondary low-emission system alongside a conventional combustion engine for cruising. An APEX-based propulsion system could replace this dual setup with a single adaptive engine that delivers full power during ocean travel and seamlessly switches to a clean operating mode upon entering regulated zones.

Looking ahead, we recognise that the space industry is expanding rapidly. Ambitious future scenarios like space mining will require a dramatic reduction in the cost per kilogram to orbit, while the defence sector demands fast response capabilities—such as the ability to rapidly replace satellites if one is taken out. APEX is designed to address both of these challenges. Our vision is to make space launches resemble aircraft operations rather than modern rocketry, where every launch is a logistical nightmare. With a spaceplane powered by APEX, takeoff could become a high-frequency, low-complexity operation—making space not only cheaper but operationally routine.